These valves usually comprise a tapered plug located within a similarly tapered housing or valve seat; said plug has a passageway for allowing fluid flow when in an open position.
These valves work in two positions: "closed" when the walls of the tapered plug shut-off the flow of the fluid through the valve and "open" when rotating the plug 90.degree. (one quarter of a turn), to provide for the passageway to become aligned with the coaxial passageway of the pipeline, thus allowing the continued flow of the fluid.
The space between the tapered plug and its tapered seat is minimum to provide for hermetism and high pressure lubrication. The thickness of the lubricant film between the plug and seat is of thousands of an inch. Therefore, a failure in lubraication will produce contact between both parts. When the failure in lubrication exceeds certain limits, the plug gets tightened with its seat. To prevent this, the development of this kind of valve has aimed toward the following objectives:
(1) To provide a pressurized lubrication; (2) to obtain precise control of plug axial movements to prevent contact between the plug and its seat by unbalancing; (3) to provide an identical pressure in upper and lower ends of the plug by means of a system that compensates the excess pressure at one end with the lack of pressure at the other end; (4) do not reduce the life nor the quality of the valve when solving the above mentioned problems. It is also desirable to provide a valve which is long-lasting and efficient as well as easy to manufacture at the lowest possible cost.
The development of related valves is specified as follows:
U.S. Pat. No. 1,584,699--Mar. 5, 1925 Non-lubricanted valve (present concept). It discloses a bronze bushing which serves as a jacket for the plug to rotate, keeping the plug in place by means of an helicoidal spring, it is a bottom entry plug valve. It has grooves for lubrication in the walls. It has a check valve that allows the pressure to flow to the bottom (larger diameter tapered side) in openning position and pushing the plug to its seat, the same than the spring, both providing tightening.
U.S. Pat. No. 1,680,812--Aug. 14, 1928 Non-lubricated valve, directional at 90.degree.. It refers to a dynamic balance mechanism similar to the idea of the present dynamic balance (see U.S. Pat. No. 4,174,092) by means of two holes which connect the port with upper and lower chambers of the plug, it has an helicoidal spring to keep the plug pisitioned with respect to the body, causing tightening and a excentric cam type system for closing the valve.
U.S. Pat. No. 1,671,603--May 29, 1928 Lubricated valve. Dynamic balace patent, obtained when the pressure of the plug's upper and lower chambers is made even. The communication of the upper chamber is obtained through a hole in the body, preventing sealant leakage by means of a check valve. This, in part, is similar to the new dynamic balance design. (see U.S. Pat. No. 4,174,092).
U.S. Pat. No. 2,079,774--May 11, 1937 Lubricated valve. It discloses plug balance through the action of 2 pistons connected to the plug mechanism (equalizer type), the reciprocating action of the pistons is obtained by the fluid pressure which helps separation and minimizes the tightening rotating force.
U.S. Pat. No. 2,286,689--June 16, 1942 Lubricated valve. It discloses the plug balance by balancing the pressure in both ends of the plug which is obtained by the flow of fluid pressure, first to the lower chamber (larger side) and then through a lateral hole in the plug which carries the pressure to the sealant chamber, and to prevent the sealant from leaking there is a check valve.
U.S. Pat. No. 2,945,668--July 19, 1960 Lubraicated valve. Bottom entry plug valve which has a sealant chamber similar to the present one. It discloses a dynamic balance produced by pressure difference between fluid and atmospheric pressures. Both plug ends are exposed to atmospheric pressure. It has no adjustable screw, instead it has a spring which positions the plug and allows its movement.
U.S. Pat. No. 3,115,151--December 24, 1963 Lubricated valve. It discloses a pressure balance between the fluid side valve, the plug passageway in closed position and the plug chamber at the larger diameter side, it uses a sling valve placed in the plug, thus making pressures even, and the plug balance is complemented with the sealant at the chamber.
U.S. Pat. No. 4,135,544--June 23, 1979 Lubricated valve. (Dynamic balance 1st option). The balance is provided by an helicoidal spring in the sealing chamber, and the larger diameter of the tapered plug is exposed to the atmospheric pressure, obtaining the balance by pressure difference.
U.S. Pat. No. 4,174,092 discloses an hydraulic balance valve which compensates the variations in the line pressure. When the pressure in the upper chamber diminishes to a pressure below to that of the line pressure, a check valve opens and thereby allows passage of the line pressure to said upper chamber, thus conpensating both pressures and thereby preventing valve lock up.